A man shot and killed an infant and critically wounded a toddler inside a Texas hotel room in the US before being arrested by officers who had been called to check on the boys and their mother, police said.

Officers still were looking for the boys' 28-year-old mother, Brandy Cerny, and "fearing the worst," Laredo Police spokesman Joe Baeza said several hours after the shooting at the Holiday Inn-Civic Center.

Police went to the hotel about midday after receiving a call from police in El Campo, a city more than 300 kilometres northeast of Laredo, saying that Cerny may have checked in there and that the family might be in some kind of trouble, Baeza said.

The desk clerk directed officers to a room on the 14th floor, where they knocked, identified themselves as police and immediately heard several shots, Baeza said. Some of the shots came through the room's door, he said.

Police cleared the building, which was packed with a convention, then entered the room and arrested the man. Baeza said the man's relationship to the family wasn't immediately clear and that he didn't speak to officers before his arrest.

The infant was declared dead at the scene, while the toddler was taken to a hospital and remained on life support Tuesday evening, Baeza said.